This is my gravity furnace. It came with the house. Actually, it was installed when the house was built in the early 1920s. It was made by the Guelph Stove Company. It still works pretty well nearly 90 years after it was put together. It was converted from oil to gas in the 1950s.
Gravity furnaces work because hot air rises. The ducts are huge and the air vents and cold air returns are pretty big too. There's no blower or fan; the flames heat these big ceramic plates, which heat the air in the big chamber. The best thing is it's quiet --- you can only tell the furnace has been on when the valve ratchets off.
I turned it on for the first time last night, since it was about 5C (that's about 40F). Here are the steps: 1) turn the thermostat up to 25C, 2) turn valve A (for the pilot), 3) prop open the burner door, 4) undo the access plate to the pilot, 5) light the pilot by getting down on my back on the dirty basement floor and holding a candle flame up to the gas jet area, 6) turn valve B (that supplies the on-off valve/thermostat thing, I think), 7) turn the electric switch on, and 8) turn the thermostat to where I want it (17C).
It was over 20C in the house this morning, which is just too hot for me these days, so I turned it down to 15C. The real house temp according to my Lee Valley thermometer is about 18-19. But this spring I installed it outside in the front window so I know how to dress in the morning. Now I need a new thermometer for inside the house.
Tips for making fruit preserves: Every time you take a step in making the jam or jelly, re-read the instructions in their entirety. Then read them again. That's how I fuxed up the grape jelly that didn't jell. I did everything right except I heated the grape juice before I stirred in the pectin crystals. Reprocessing worked very well, though, except I started with 9 jars of juice, added 1/2 cup of sugar, 1 1/2 cups of water, and ended up with 8 jars of perfect jelly. Go figure.